A cnidarian homologue of an insect gustatory receptor functions in developmental body patterning

Insect gustatory and odorant receptors (GRs and ORs) form a superfamily of novel transmembrane proteins, which are expressed in chemosensory neurons that detect environmental stimuli. Here we identify homologues of GR s ( Gustatory receptor-like ( Grl ) genes) in genomes across Protostomia, Deuterostomia and non-Bilateria. Surprisingly, two Grls in the cnidarian Nematostella vectensis , NvecGrl1 and NvecGrl2 , are expressed early in development, in the blastula and gastrula, but not at later stages when a putative chemosensory organ forms. NvecGrl1 transcripts are detected around the aboral pole, considered the equivalent to the head-forming region of Bilateria. Morpholino-mediated knockdown of NvecGrl1 causes developmental patterning defects of this region, leading to animals lacking the apical sensory organ. A deuterostome Grl from the sea urchin Strongylocentrotus purpuratus displays similar patterns of developmental expression. These results reveal an early evolutionary origin of the insect chemosensory receptor family and raise the possibility that their ancestral role was in embryonic development. Insect gustatory and olfactory receptor genes encode transmembrane proteins that detect diverse chemicals, but their evolutionary origins are unclear. This study identifies homologues of these genes in non-Bilateria and reveals an unexpected role for one in sea anemone embryonic development.